The present invention relates to a pressure electrolyzer, and to a method of operating said pressure electrolyzer.
Pressure electrolyzers are known for the eletrolytic splitting-up of water into hydrogen and oxygen. Such known pressure electrolyzers comprise a pressure vessel and an electrolytic-cell block, which is arranged in said pressure vessel and contains a plurality of electrolytic cells which are combined in the form of a stack. The electrolytic cells in each case contain anodes and cathodes, and an electrolyte-circuit system is provided for supplying an anolyte to the anodes and for supplying a catholyte to the cathodes. The electrolytic-cell block comprises a housing which is sealed relative to the interior of the pressure vessel.
A pressure electrolyzer of this description is known from German Publication DE 25 48 699 C3. In the case of this known pressure electolyzer, means for the purification, cooling and circulation of the electrolyte are also arranged in the pressure vessel in addition to the electrolytic-cell block.
An object of the invention is to provide an improved pressure electrolyzer. Furthermore, an improved method of operating such a pressure electrolyzer is to be described.
As far as the apparatus is concerned, this object is met by the claimed pressure electrolyzer.
Advantageous further developments of the pressure electolyzer according to the invention are set out in the dependent claims.
As far as the method is concerned, the set object is met by the claimed method. Advantageous further developments of the method according to the invention are set out in the dependent claims.
The invention provides a pressure electrolyzer which comprises a pressure vessel and an electrolytic-cell block which is arranged in the pressure vessel and contains a plurality of electrolytic cells combined in the form of a stack. The electrolytic cells in each case contain anodes and cathodes, and an electrolyte-circuit system is provided for supplying an anolyte to the anodes and for supplying a catholyte to the cathodes. The electrolytic-cell block comprises a housing which is sealed relative to the interior of the pressure vessel. It is provided, according to the invention, that the housing of the electrolytic-cell block, together with the pressure vessel, forms at least two chambers, which are separated from each other, which constitute a part of the electrolyte-circuit system and which are defined relative to the electrolytic cells by the housing and relative to the atmosphere by the pressure vessel. An advantage of the pressure electrolyzer according to the invention is the simplicity of the design of the electrolyte-circuit system. A further advantage is that relatively little space is required by the pressure electrolyzer according to the invention.
According to a particularly preferred embodiment of the pressure electrolyzer according to the invention, one of the chambers, being separated from the other chamber, constitutes a part of an anolyte circuit, and the other chamber, being separated from said one chamber, constitutes a part of a catholyte circuit. An advantage of this embodiment is that, by separating the anolyte and catholyte circuits, it is possible to achieve a higher degree of gas purity and, consequently, a wider range of load control.
A particularly preferred embodiment of the pressure electrolyzer according to the invention provides that the chambers which are separated from each other are separated by separating walls which extend between the housing and the pressure vessel.
According to a preferred embodiment, the pressure vessel has the shape of a cylinder and the longitudinal axis of the electrolytic-cell block is arranged in the pressure vessel parallel with the axis of the cylinder.
According to a further preferred embodiment of the pressure electrolyzer according to the invention, the separating walls extend between the housing and the pressure vessel parallel with the axis of the cylinder.
According to a particularly preferred embodiment of the pressure electrolyzer according to the invention, the housing of the electrolytic-cell block is composed of a plurality of cell frames of the electrolytic cells, which cell frames are stacked side by side.
According to an advantageous further development in this regard, it is provided that, in each case, each anode has its own anode cell frame and, in each case, each cathode has its own cathode cell frame, and that the anode cell frames comprise passages, which produce a connection between the anode and the chamber which constitutes a part of the anolyte circuit, and that the cathode cell frames comprise passages which produce a connection between the cathode and the chamber which constitutes a part of the catholyte circuit.
A further advantageous embodiment provides that the electrolytic-cell block is arranged with its longitudinal direction substantially horizontally, and that that chamber, which is defined by the housing of the electrolytic-cell block and the pressure vessel, is vertically subdivided in the longitudinal direction of the electrolytic-cell block into the two chambers which are separated from each other.
A particularly advantageous further development of the two last-mentioned embodiments provides that the passages producing a connection with the anodes are in communication, in each case on the upper side and on the lower side of the anode cell frames, with the one of the chambers, which is separated from the other chamber and constitutes a part of the anolyte circuit, and that the passages producing a connection with the cathodes are in communication, in each case on the upper side and on the lower side of the cathode cell frames with the other of the chambers, which is separated from said one chamber and constitutes a part of the catholyte circuit. The advantage hereof is that it is possible for the electrolyte to circulate automatically without an additional electrolyte-circuit pump, due to a gas lift effect because of the gases rising in the cells and the lower density of the electrolyte/gas mixture in the cells, relative to the degassed electrolyte columns outside the cells. The product gases oxygen, respectively hydrogen, collect along the crowns of the two chambers which are separated from each other.
According to a further advantageous embodiment of the pressure electrolyzer according to the invention, essential components of the electrolyte-circuit system, in particular a gas separator and/or an electrolyte cooler, are provided within the pressure vessel. The advantage hereof is a particularly space-saving, compact design of the pressure electrolyzer.
According to a further advantageous embodiment, one of the separating walls is arranged below the electrolytic-cell block and simultaneously forms a mechanical support for said block.
A particularly advantageous embodiment of the pressure electrolyzer according to the invention provides that the anodes and cathodes are encircled by a sealing element, which extends about their periphery and which forms a lateral end of the electrolytic cell in the region of the anode, respectively of the cathode, and which is sealingly fitted between the cell frames.
A particularly preferred embodiment hereof provides that the anode and the cathode of an electrolytic cell are each separately encircled in a sealing element.
The sealing elements of the anode and the cathode are preferably jointly sealingly fitted between two successive cell frames.
The sealing elements preferably also form a lateral end of the electrolytic cell on a diaphragm which is arranged between the anode and the cathode.
The diaphragm is preferably sealingly fitted between the sealing element of the anode and the sealing element of the cathode.
The sealing elements are preferably arranged about the periphery of the anode and/or of the cathode so as to extend in the manner of a frame.
According to a preferred embodiment, it is provided that the sealing elements are designed to be led about the edge of the anode and/or of the cathode from the front side to the rear side of said anode and/or said cathode.
According to a particularly advantageous embodiment hereof, the sealing elements are provided with one or more sealing lips, which extend about the periphery of the anode, respectively of the cathode, and which rest sealingly against a sealing face of the anode cell frame, respectively of the cathode cell frame.
It is preferably provided, in this regard, that the sealing lips project in a perpendicular direction relative to the flat side of the anode, respectively of the cathode, and that the sealing faces of the anode cell frame, respectively of the cathode cell frame, are designed to extend parallel to the flat side of the anode, respectively of the cathode.
The sealing elements are preferably produced from an elastomer.
In this regard, it is particularly advantageous when the sealing elements are produced by extrusion-coating of the edge of the anode, respectively of the cathode, using the elastomer.
According to an advantageous further development of the pressure electrolyzer according to the invention, two adjacent electrolytic cells are separated from each other by a bipolar metal sheet which is encircled by a sealing element, which extends about the periphery of said bipolar metal sheet and forms a lateral end of the electrolytic cell in the region of the bipolar metal sheet and is sealingly fitted between the cell frames of the adjacent electrolytic cells.
The sealing element is preferably arranged to extend about the periphery of the bipolar metal sheet in the manner of a frame.
According to an embodiment, the sealing element is arranged on one side of the bipolar metal sheet.
According to another embodiment, the sealing element is designed to be led about the edge of the bipolar metal sheet, from the front side to the rear side thereof.
According to a preferred embodiment, the sealing element is provided with one or more sealing lips which extend about the periphery of the bipolar metal sheet and rest sealingly against a sealing face of the anode cell frame, respectively of the cathode cell frame, or against the bipolar metal sheet itself.
A preferred embodiment hereof provides that the sealing lips project in a perpendicular direction relative to the flat side of the bipolar metal sheet, and that the sealing face of the anode cell frame, respectively of the cathode cell frame, is designed to extend parallel to the flat side of the bipolar metal sheet.
The sealing element is preferably produced from an elastomer.
It is possible for the sealing element to be produced by extrusion-coating of the edge of the bipolar metal sheet using the elastomer.
The separate chambers in the pressure vessels are, according to an advantageous development, connected to each other at a geodetically low point so as to permit an alignment of the levels between the anolyte and the catholyte. The connection is provided by a connecting pipe which extends outside the pressure vessel. By way of alternative, it is possible for the chambers within the pressure vessel to communicate via an opening or a membrane in the separating means.
For the purpose of the electrical insulation, the pressure vessel is, according to an embodiment, of an electrically non-conductive material. By way of alternative, each of the chambers defined by the housing of the electrolytic-cell block and the inner side of the pressure vessel are encapsulated by a shell of an electrically insulating material. It is also possible for the housing of the electrolytic-cell block and/or the pressure vessel to be provided with an electrically insulating coating or lining.
The separation of the gas takes place within the pressure vessel in regions disposed geodetically above the electrolytic-cell block. It is advantageous, in this regard, to arrange gas-coalescing aids, in the form of knit fabrics and/or ultrasonic transmitters and/or flow-deflecting means in the gas-separating regions.
According to a further development of the pressure electrolyzer according to the invention, a water-supply tank is provided. The water-supply tank is connected to a feed-water source via a feed-water filling pipe comprising a feed-water fill-up valve, to a bottom region of one of the separated chambers via a feed-water inflow pipe comprising a feed-water inflow valve, and to a top region of the one of the separated chambers via a pressurizing pipe comprising a pressurizing valve. The water-supply tank, additionally, can be evacuated relative to the atmosphere via a ventilation pipe comprising a ventilation valve, the top region of the one of the separated chambers being filled, during operation of the pressure electrolyzer, with one of the product gases.
According to an advantageous embodiment, it is provided that the one of the separated chambers, to which the water-supply tank is connected via the feed-water inflow pipe and via the pressurizing pipe, is the other separated chamber constituting a part of the electrolyte circuit.
As far as the method is concerned, the set object is met by a method of filling a pressure electrolyzer according to the two last-mentioned embodiments, including the following method steps:
a) pressure-free filling of the water-supply tank via the feed-water filling pipe with the feed-water fill-up valve open, while the ventilation valve is open, the pressurizing valve is closed and the feed-water inflow valve is closed,
b) closing the ventilation valve and the feed-water fill-up valve,
c) opening the pressurizing valve, so as to bring the water-supply tank to the pressure prevailing in the pressure vessel via the pressurizing pipe,
d) opening the feed-water inflow valve, so as to admit metered quantities of feed water from the supply tank into the pressure vessel, and
e) closing the feed-water inflow valve.
The metered addition of the feed water from the supply tank into the pressure vessel preferably takes place under gravity, the water-supply tank being arranged spatially above the pressure vessel.
By way of alternative, it is also possible for the metered addition of the feed water from the water-supply tank into the pressure vessel to be carried out by means of a feed-water pump included in the feed-water inflow pipe, which pump may then advantageously have a low capacity.